Arginine-rich cell-penetrating peptides

Thermoresponsive Collagen/Cell Penetrating Hybrid Peptide as Nanocarrier in Targeting-Free Cell Selection and Uptake

The effective delivery of therapeutics and imaging agents to a selected group of cells has been at the forefront of biomedical research. Unfortunately, the identification of the unique cell surface targets for cell selection remains a major challenge, particularly if cells within the selected group are not identical. Here we demonstrate a novel approach to cell section relying on a thermoresponsive peptide-based nanocarrier. The hybrid peptide containing cell-penetrating peptide (CPP) and collagen (COLL) domains is designed to undergo coil-to-helix transition (folding) below physiological temperature. Because only the helical form undergoes effective internalization by the cells, this approach allows effective temperature-discriminate cellular uptake. The cells selected for uptake are locally cooled, thus enabling the carrier to fold and subsequently internalize. Our approach demonstrates a generic method as selected cells could differ from the adjacent cells or could belong to the same cell population. The method is fast (<15 min) and selective; over 99.6% of cells in vitro internalized the peptide carrier at low temperatures (15 °C), while less than 0.2% internalized at 37 °C. In vivo results confirm the high selectivity of the method. The potential clinical applications in mixed cell differentiation carcinoma, most frequently encountered in breast and ovarian cancer, are envisioned.

Focused Library Approach to Discover Discrete Dipeptide Bolaamphiphiles for siRNA Delivery

In this study, we report a new dipeptide functionalization strategy for developing new dendritic bolaamphiphile vectors for efficient siRNA transfection. A focused library of dipeptides was constructed using four amino acids: l-arginine, l-histidine, l-lysine, and l-tryptophan. The dipeptides were coupled to two dendritic bolaamphiphile scaffolds that we developed previously, allowing us to quickly access a focused library of discrete vectors with multivalent dendritic dipeptide functionalities. The resulting discrete bolaamphiphiles were screened for siRNA delivery in vitro in HEK-293 and HeLa cells. Bolaamphiphiles functionalized with dipeptides containing Lys or Arg and either His or Trp were the most effective for in vitro siRNA delivery. Necessary cationic charge to ensure efficient siRNA binding are provided by Arg and Lys residues, whereas endosomal escape is provided through pH responsive buffering of His or membrane interactions of Trp. The most effective vectors (F10 HR/RH) exhibited greater than 75% gene silencing in multiple cell lines and exhibited serum stability.

Delivery of nucleic acids for cancer gene therapy: overcoming extra- and intra-cellular barriers

The therapeutic potential of cancer gene therapy has been limited by the difficulty of delivering genetic material to target sites. Various biological and molecular barriers exist which need to be overcome before effective nonviral delivery systems can be applied successfully in oncology. Herein, various barriers are described and strategies to circumvent such obstacles are discussed, considering both the extracellular and intracellular setting. Development of multifunctional delivery systems holds much promise for the progression of gene delivery, and a growing body of evidence supports this approach involving rational design of vectors, with a unique molecular architecture. In addition, the potential application of composite gene delivery platforms is highlighted which may provide an alternative delivery strategy to traditional systemic administration.

Protein transduction therapy into cochleae via the round window niche in guinea pigs

Cell-penetrating peptides (CPPs) are short sequences of amino acids that facilitate the penetration of conjugated cargoes across mammalian cell membranes, and as such, they may provide a safe and effective method for drug delivery to the inner ear. Simple polyarginine peptides have been shown to induce significantly higher cell penetration rates among CPPs. Herein, we show that a peptide consisting of nine arginines ("9R") effectively delivered enhanced green fluorescent protein (EGFP) into guinea pig cochleae via the round window niche without causing any deterioration in auditory function. A second application, 24 hours after the first, prolonged the presence of EGFP. To assess the feasibility of protein transduction using 9R-CPPs via the round window, we used "X-linked inhibitor of apoptosis protein" (XIAP) bonded to a 9R peptide (XIAP-9R). XIAP-9R treatment prior to acoustic trauma significantly reduced putative hearing loss and the number of apoptotic hair cells loss in the cochleae. Thus, the topical application of molecules fused to 9R-CPPs may be a simple and promising strategy for treating inner ear diseases.

Effects of protein transduction domain (PTD) selection and position for improved intracellular delivery of PTD-Hsp27 fusion protein formulations

Protein drugs have attracted considerable attention as therapeutic agents due to their diversity and biocompatibility. However, hydrophilic proteins possess difficulty in penetrating lipophilic cell membrane. Although protein transduction domains (PTDs) have shown effectiveness in protein delivery, the importance of selection and position of PTDs in recombinant protein vector constructs has not been investigated. This study intends to investigate the significance of PTD selection and position for therapeutic protein delivery. Heat shock protein 27 (Hsp27) would be a therapeutic protein for the treatment of ischemic heart diseases, but itself is insufficient to prevent systemic degradation and overcoming biochemical barriers during cellular transport. Among all PTD-Hsp27 fusion proteins we cloned, Tat-Hsp27 fusion protein showed the highest efficacy. Nona-arginine (9R) conjugation to the N-terminal of Hsp27 (Hsp27-T) showed higher efficacy than C-terminal. To test the synergistic effect of two PTDs, Tat was inserted to the N-terminal of Hsp27-9R. Tat-Hsp27-9R exhibited enhanced transduction efficiency and significant improvement against oxidative stress and apoptosis. PTD-Hsp27 fusion proteins have strong potential to be developed as therapeutic proteins for the treatment of ischemic heart diseases and selection and position of PTDs for improved efficacy of PTD-fusion proteins need to be optimized considering protein’s nature, transduction efficiency and stability.

Effect of poly-glutamate on uptake efficiency and cytotoxicity of cell penetrating peptides

Cell penetrating peptides (CPPs) were developed as vehicles for efficient delivery of various molecules. An ideal CPP-peptide should not display any toxicity against cancer cells as well as healthy cells and efficiently enter into the cell. Because of the cationic nature and the intrinsic vector capabilities, these peptides can cause cytotoxicity. One of the possible reasons for toxicity of CPPs is direct translocation and consequently, pore formation on the plasma membrane. In this study it was demonstrated that interaction of poly-glutamate with CPP considerably reduced their cytotoxicity in A549 cell. This strategy could be useful for efficient drug delivery mediated by CPP.

The Role of Cell-Penetrating Peptide and Transferrin on Enhanced Delivery of Drug to Brain

The challenge of effectively delivering therapeutic agents to brain has led to an entire field of active research devoted to overcome the blood brain barrier (BBB) and efficiently deliver drugs to brain. This review focusses on exploring the facets of a novel platform designed for the delivery of drugs to brain. The platform was constructed based on the hypothesis that a combination of receptor-targeting agent, like transferrin protein, and a cell-penetrating peptide (CPP) will enhance the delivery of associated therapeutic cargo across the BBB. The combination of these two agents in a delivery vehicle has shown significantly improved (p < 0.05) translocation of small molecules and genes into brain as compared to the vehicle with only receptor-targeting agents. The comprehensive details of the uptake mechanisms and properties of various CPPs are illustrated here. The application of this technology, in conjunction with nanotechnology, can potentially open new horizons for the treatment of central nervous system disorders.

Cell-permeable p38 MAP kinase promotes migration of adult neural stem/progenitor cells

Endogenous neural stem/progenitor cells (NPCs) can migrate toward sites of injury, but the migration activity of NPCs is insufficient to regenerate damaged brain tissue. In this study, we showed that p38 MAP kinase (p38) is expressed in doublecortin-positive adult NPCs. Experiments using the p38 inhibitor SB203580 revealed that endogenous p38 participates in NPC migration. To enhance NPC migration, we generated a cell-permeable wild-type p38 protein (PTD-p38WT) in which the HIV protein transduction domain (PTD) was fused to the N-terminus of p38. Treatment with PTD-p38WT significantly promoted the random migration of adult NPCs without affecting cell survival or differentiation; this effect depended on the cell permeability and kinase activity of the fusion protein. These findings indicate that PTD-p38WT is a novel and useful tool for unraveling the roles of p38, and that this protein provides a reasonable approach for regenerating the injured brain by enhancing NPC migration.

Antifungal mechanisms of a plant defensin MtDef4 are not conserved between the ascomycete fungi Neurospora crassa and Fusarium graminearum

Defensins play an important role in plant defense against fungal pathogens. The plant defensin, MtDef4, inhibits growth of the ascomycete fungi, Neurospora crassa and Fusarium graminearum, at micromolar concentrations. We have reported that MtDef4 is transported into the cytoplasm of these fungi and exerts its antifungal activity on intracellular targets. Here, we have investigated whether the antifungal mechanisms of MtDef4 are conserved in these fungi. We show that N. crassa and F. graminearum respond differently to MtDef4 challenge. Membrane permeabilization is required for the antifungal activity of MtDef4 against F. graminearum but not against N. crassa. We find that MtDef4 is targeted to different subcellular compartments in each fungus. Internalization of MtDef4 in N. crassa is energy-dependent and involves endocytosis. By contrast, MtDef4 appears to translocate into F. graminearum autonomously using a partially energy-dependent pathway. MtDef4 has been shown to bind to the phospholipid phosphatidic acid (PA). We provide evidence that the plasma membrane localized phospholipase D, involved in the biosynthesis of PA, is needed for entry of this defensin in N. crassa, but not in F. graminearum. To our knowledge, this is the first example of a defensin which inhibits the growth of two ascomycete fungi via different mechanisms.

Interaction of peptides with cell membranes: insights from molecular modeling

The investigation of the interaction of peptides with cell membranes is the focus of active research. It can enhance the understanding of basic membrane functions such as membrane transport, fusion, and signaling processes, and it may shed light on potential applications of peptides in biomedicine. In this review, we will present current advances in computational studies on the interaction of different types of peptides with the cell membrane. Depending on the properties of the peptide, membrane, and external environment, the peptide-membrane interaction shows a variety of different forms. Here, on the basis of recent computational progress, we will discuss how different peptides could initiate membrane pores, translocate across the membrane, induce membrane endocytosis, produce membrane curvature, form fibrils on the membrane surface, as well as interact with functional membrane proteins. Finally, we will present a conclusion summarizing recent progress and providing some specific insights into future developments in this field.

Inhibition of cell proliferation, migration and invasion by a glioma-targeted fusion protein combining the p53 C terminus and MDM2-binding domain

OBJECTIVES

The aim of this study was to develop multifunctional fusion proteins for targeting and delivering therapy elements into glioma cells.

MATERIALS AND METHODS

Multifunctional fusion proteins were expressed in Escherichia coli and purified using Ni-NTA resin affinity chromatography. Human glioma cells and primary astrocytes were used to analyse their functions. Targeting proteins location to glioma cells was observed by confocal microscopy. Effects of cell viability and proliferation were evaluated using the Cell Counting Kit 8 and colony formation assays. Glioma cell migration and invasion were assessed using transwell assays, and apoptosis was analysed by flow cytometry. In addition, changes in expression of proteins related to the cell cycle and apoptosis were determined by Western blotting.

RESULTS

The protein with highest bioactivity was GL1-riHA2-p53c+m-TAT (GHPc+mT), which combines glioma-targeting peptide GL1 (G), and C terminus (Pc) and mouse double minute domains (Pm) of p53, with the destabilizing lipid membrane peptide riHA2 (H) and cell-penetrating peptide TAT (T). The purified fusion protein was stable in cell culture medium and specifically targeted, and was internalized by, epidermal growth factor receptor (EGFR)-overexpressing glioma cells (U87ΔEGFR). It inhibited cell proliferation, migration and invasion, while flow cytometric analysis showed increased apoptosis. In addition, GHPc+mT caused significant changes in expression of proteins related to the cell cycle and apoptosis.

CONCLUSION

GHPc+mT is a multifunctional protein combining targeting, inhibition of glioma cell proliferation and induction of apoptosis, providing some potential to be developed into an effective protein drug delivery system for glioma therapy.

A Cell-Penetrating Peptide with a Guanidinylethyl Amine Structure Directed to Gene Delivery

A peptide composed of lysine with a guanidinylethyl (GEt) amine structure in the side chain [Lys(GEt)] was developed as a cell-penetrating peptide directed to plasmid DNA (pDNA) delivery. The GEt amine adopted a diprotonated form at neutral pH, which may have led to the more efficient cellular uptake of a Lys(GEt)-peptide than an arginine-peptide at a low concentration. Lys(GEt)-peptide/pDNA complexes showed the highest transfection efficiency due to efficient endosomal escape without any cytotoxicity. Lys(GEt)-peptide may be a promising candidate as a gene delivery carrier.

Interactions of a class IIb bacteriocin with a model lipid bilayer, investigated through molecular dynamics simulations

The emergence of antibiotic resistant microorganisms poses an alarming threat to global health. Antimicrobial peptides (AMPs) are considered a possible effective alternative to conventional antibiotic therapies. An understanding of the mechanism of action of AMPs is needed in order to better control and optimize their bactericidal activity. Plantaricin EF is a heterodimeric AMP, consisting of two peptides Plantaricin E (PlnE) and Plantaricin F (PlnF). We studied the behavior of these peptides on the surface of a model lipid bilayer. We identified the residues that facilitate peptide-peptide interactions. We also identified residues that mediate interactions of the dimer with the membrane. PlnE interacts with the membrane through amino acids at both its termini, while only the N terminus of PlnF approaches the membrane. By comparing the activity of single-site mutants of the two-peptide bacteriocin and the simulations of the bacteriocin on the surface of a model lipid bilayer, structure activity relationships are proposed. These studies allow us to generate hypotheses that relate biophysical interactions observed in simulations with the experimentally measured activity. We find that single-site amino acid substitutions result in markedly stronger antimicrobial activity when they strengthen the interactions between the two peptides, while, concomitantly, they weaken peptide-membrane association. This effect is more pronounced in the case of the PlnE mutant (G20A), which interacts the strongest with PlnF and the weakest with the membrane while displaying the highest activity.

Archetypal tryptophan-rich antimicrobial peptides: properties and applications

Drug-resistant microorganisms ('superbugs') present a serious challenge to the success of antimicrobial treatments. Subsequently, there is a crucial need for novel bio-control agents. Many antimicrobial peptides (AMPs) show a broad-spectrum activity against bacteria, fungi or viruses and are strong candidates to complement or substitute current antimicrobial agents. Some AMPs are also effective against protozoa or cancer cells. The tryptophan (Trp)-rich peptides (TRPs) are a subset of AMPs that display potent antimicrobial activity, credited to the unique biochemical properties of tryptophan that allow it to insert into biological membranes. Further, many Trp-rich AMPs cross bacterial membranes without compromising their integrity and act intracellularly, suggesting interactions with nucleic acids and enzymes. In this work, we overview some archetypal TRPs derived from natural sources, i.e., indolicidin, tritrpticin and lactoferricin, summarising their biochemical properties, structures, antimicrobial activities, mechanistic studies and potential applications.

Comparative density functional theory and density functional tight binding study of arginine and arginine-rich cell penetrating peptide TAT adsorption on anatase TiO2

A comparative DFT-DFTB study of geometries and electronic structures of arginine, arginine dipeptide, and arginine-rich cell penetrating peptide TAT on the surface of TiO₂.

Aptamer mediated niosomal drug delivery

Development of nanoscale carrier systems for targeted drug delivery is crucial for cancer treatment.

Experimental and simulation studies of polyarginines across the membrane of giant unilamellar vesicles

Cell-penetrating peptides have widespread applications in biomedicine because of their capability to translocate across cell membranes alone or with cargos.

A Copper-Mediated Disulfiram-Loaded pH-Triggered PEG-Shedding TAT Peptide-Modified Lipid Nanocapsules for Use in Tumor Therapy

Disulfiram, which exhibits marked tumor inhibition mediated by copper, was encapsulated in lipid nanocapsules modified with TAT peptide (TATp) and pH-triggered sheddable PEG to target cancer cells on the basis of tumor environmental specificity. PEG-shedding lipid nanocapsules (S-LNCs) were fabricated from LNCs by decorating short PEG chains with TATp (HS-PEG(1k)-TATp) to form TATp-LNCs and then covered by pH-sensitive graft copolymers of long PEG chains (PGA-g-PEG(2k)). The DSF-S-LNCs had sizes in the range of 60-90 nm and were stable in the presence of 50% plasma. DSF-S-LNCs exhibited higher intracellular uptake and antitumor activity at pH 6.5 than at pH 7.4. The preincubation of Cu showed that the DSF cytotoxicity was based on the accumulation of Cu in Hep G2 cells. Pharmacokinetic studies showed the markedly improved pharmacokinetic profiles of DSF-S-LNCs (AUC= 3921.391 μg/L·h, t(1/2z) = 1.294 h) compared with free DSF (AUC = 907.724 μg/L·h, t(1/2z) = 0.252 h). The in vivo distribution of S-LNCs was investigated using Cy5.5 as a fluorescent probe. In tumor-bearing mice, the delivery efficiency of S-LNCs was found to be 496.5% higher than that of free Cy5.5 and 74.5% higher than that of LNCs in tumors. In conclusion, DSF-S-LNCs increased both the stability and tumor internalization and further increased the cytotoxicity because of the higher copper content.

Mechanism Matters: A Taxonomy of Cell Penetrating Peptides

The permeability barrier imposed by cellular membranes limits the access of exogenous compounds to the interior of cells. Researchers and patients alike would benefit from efficient methods for intracellular delivery of a wide range of membrane-impermeant molecules, including biochemically active small molecules, imaging agents, peptides, peptide nucleic acids, proteins, RNA, DNA, and nanoparticles. There has been a sustained effort to exploit cell penetrating peptides (CPPs) for the delivery of such useful cargoes in vitro and in vivo because of their biocompatibility, ease of synthesis, and controllable physical chemistry. Here, we discuss the many mechanisms by which CPPs can function, and describe a taxonomy of mechanisms that could be help organize future efforts in the field.

Intrinsic cell permeability of the GAGA zinc finger protein into HeLa cells

We examined the intrinsic cell permeability of a GAGA zinc finger obtained from the Drosophila melanogaster transcription factor and analyzed its mechanism of cellular uptake using confocal microscopy and flow cytometry. HeLa cells were treated with the Cy5-labeld GAGA peptides (containing a fluorescent chromophore) to detect fluorescence signals from the fluorescent labeling peptides by confocal microscopy. The results clearly indicated that GAGA peptides possess intrinsic cell permeability for HeLa cells. Based on the results of the flow cytometry analysis and the theoretical net positive charge of the GAGA peptides, the efficiency of cellular uptake of the GAGA peptides was predicted to depend on the net positive charge of the GAGA peptide as well as the cationic component ratio of Arg residues to Lys residues.

Protein transport across membranes: Comparison between lysine and guanidinium-rich carriers

The mechanism(s) by which certain small peptides and peptide mimics carry large cargoes across membranes through exclusively non-covalent interactions has been difficult to resolve. Here, we use the droplet-interface bilayer as a platform to characterize distinct mechanistic differences between two such carriers: Pep-1 and a guanidinium-rich peptide mimic we call D9. While both Pep-1 and D9 can carry an enzyme, horseradish peroxidase (HRP) across a lipid bilayer, we found that they do so by different mechanisms. Specifically, Pep-1 requires voltage or membrane asymmetry while D9 does not. In addition, D9 can facilitate HRP transport without pre-forming a complex with HRP. By contrast, complex formation is required by Pep-1. Both carriers are capable of forming pores in membranes but our data hints that these pores are not responsible for cargo transport. Overall, D9 appears to be a more potent and versatile transporter when compared with Pep-1 because D9 does not require an applied voltage or other forces to drive transport. Thus, D9 might be used to deliver cargo across membranes under conditions where Pep-1 would be ineffective.

Identification of a cell-penetrating peptide domain from human beta-defensin 3 and characterization of its anti-inflammatory activity

Human beta-defensins (hBDs) are crucial factors of intrinsic immunity that function in the immunologic response to a variety of invading enveloped viruses, bacteria, and fungi. hBDs can cause membrane depolarization and cell lysis due to their highly cationic nature. These molecules participate in antimicrobial defenses and the control of adaptive and innate immunity in every mammalian species and are produced by various cell types. The C-terminal 15-mer peptide within hBD3, designated as hBD3-3, was selected for study due to its cell- and skin-penetrating activity, which can induce anti-inflammatory activity in lipopolysaccharide-treated RAW 264.7 macrophages. hBD3-3 penetrated both the outer membrane of the cells and mouse skin within a short treatment period. Two other peptide fragments showed poorer penetration activity compared to hBD3-3. hBD3-3 inhibited the lipopolysaccharide-induced production of inducible nitric oxide synthase, nitric oxide, and secretory cytokines, such as interleukin-6 and tumor necrosis factor in a concentration-dependent manner. Moreover, hBD3-3 reduced the interstitial infiltration of polymorphonuclear leukocytes in a lung inflammation model. Further investigation also revealed that hBD3-3 downregulated nuclear factor kappa B-dependent inflammation by directly suppressing the degradation of phosphorylated-IκBα and by downregulating active nuclear factor kappa B p65. Our findings indicate that hBD3-3 may be conjugated with drugs of interest to ensure their proper translocation to sites, such as the cytoplasm or nucleus, as hBD3-3 has the ability to be used as a carrier, and suggest a potential approach to effectively treat inflammatory diseases.

Coarse-grained molecular dynamics studies of the translocation mechanism of polyarginines across asymmetric membrane under tension

Understanding interactions between cell-penetrating peptides and biomembrane under tension can help improve drug delivery and elucidate mechanisms underlying fundamental cellular events. As far as the effect of membrane tension on translocation, it is generally thought that tension should disorder the membrane structure and weaken its strength, thereby facilitating penetration. However, our coarse-grained molecular dynamics simulation results showed that membrane tension can restrain polyarginine translocation across the asymmetric membrane and that this effect increases with increasing membrane tension. We also analyzed the structural properties and lipid topology of the tensed membrane to explain the phenomena. Simulation results provide important molecular information on the potential translocation mechanism of peptides across the asymmetric membrane under tension as well as new insights in drug and gene delivery.

Aib-containing peptide analogs: cellular uptake and utilization in oligonucleotide delivery

α-Aminoisobutyric acid (Aib)-containing peptide analogs derived from TV-XIIa, a cell-penetrating peptide (CPP), were synthesized to explore structure-activity relationships. The replacement of Aib at position 1, 5, or 9 in the TV-XIIa amino acid sequence with alanine (Ala) suppressed the cellular uptake,whereas the simultaneous substitution of the two proline (Pro) residues at positions 6 and 10 with Aib(P-IV) considerably increased the cellular uptake. In order to explore the potential use of the Aib-containing peptide analogs for the cellular delivery of oligonucleotides (ODNs), we synthesized a covalent conjugate (P-IV-AON) of a 15-mer antisense ODN, which is complementary to luciferase gene, with P-IV, and the antisense effect of the P-IV-AON conjugate on luciferase expression in A549 cells was examined. Luciferase expression was decreased in the presence of the conjugate upon treatment with the reaction buffer at the concentrations of 5 and 10 μM.

Investigating Hydrophilic Pores in Model Lipid Bilayers Using Molecular Simulations: Correlating Bilayer Properties with Pore-Formation Thermodynamics

Cell-penetrating and antimicrobial peptides show a remarkable ability to translocate across physiological membranes. Along with factors such as electric-potential-induced perturbations of membrane structure and surface tension effects, experiments invoke porelike membrane configurations during the solute transfer process into vesicles and cells. The initiation and formation of pores are associated with a nontrivial free-energy cost, thus necessitating a consideration of the factors associated with pore formation and the attendant free energies. Because of experimental and modeling challenges related to the long time scales of the translocation process, we use umbrella sampling molecular dynamics simulations with a lipid-density-based order parameter to investigate membrane-pore-formation free energy employing Martini coarse-grained models. We investigate structure and thermodynamic features of the pore in 18 lipids spanning a range of headgroups, charge states, acyl chain lengths, and saturation. We probe the dependence of pore-formation barriers on the area per lipid, lipid bilayer thickness, and membrane bending rigidities in three different lipid classes. The pore-formation free energy in pure bilayers and peptide translocating scenarios are significantly coupled with bilayer thickness. Thicker bilayers require more reversible work to create pores. The pore-formation free energy is higher in peptide-lipid systems than in peptide-free lipid systems due to penalties to maintain the solvation of charged hydrophilic solutes within the membrane environment.

Inhibition of N-Methyl-D-aspartate-induced Retinal Neuronal Death by Polyarginine Peptides Is Linked to the Attenuation of Stress-induced Hyperpolarization of the Inner Mitochondrial Membrane Potential

It is widely accepted that overactivation of NMDA receptors, resulting in calcium overload and consequent mitochondrial dysfunction in retinal ganglion neurons, plays a significant role in promoting neurodegenerative disorders such as glaucoma. Calcium has been shown to initiate a transient hyperpolarization of the mitochondrial membrane potential triggering a burst of reactive oxygen species leading to apoptosis. Strategies that enhance cell survival signaling pathways aimed at preventing this adverse hyperpolarization of the mitochondrial membrane potential may provide a novel therapeutic intervention in retinal disease. In the retina, brain-derived neurotrophic factor has been shown to be neuroprotective, and our group previously reported a PSD-95/PDZ-binding cyclic peptide (CN2097) that augments brain-derived neurotrophic factor-induced pro-survival signaling. Here, we examined the neuroprotective properties of CN2097 using an established retinal in vivo NMDA toxicity model. CN2097 completely attenuated NMDA-induced caspase 3-dependent and -independent cell death and PARP-1 activation pathways, blocked necrosis, and fully prevented the loss of long term ganglion cell viability. Although neuroprotection was partially dependent upon CN2097 binding to the PDZ domain of PSD-95, our results show that the polyarginine-rich transport moiety C-R(7), linked to the PDZ-PSD-95-binding cyclic peptide, was sufficient to mediate short and long term protection via a mitochondrial targeting mechanism. C-R(7) localized to mitochondria and was found to reduce mitochondrial respiration, mitochondrial membrane hyperpolarization, and the generation of reactive oxygen species, promoting survival of retinal neurons.

Quantum dot-based molecular beacon to monitor intracellular microRNAs

Fluorescence monitoring of endogenous microRNA (miRNA or miR) activity related to neuronal development using nano-sized materials provides crucial information on miRNA expression patterns in a noninvasive manner. In this study, we report a new method to monitor intracellular miRNA124a using quantum dot-based molecular beacon (R9-QD-miR124a beacon). The R9-QD-miR124a beacon was constructed using QDs and two probes, miR124a-targeting oligomer and arginine rich cell-penetrating peptide (R9 peptide). The miR124a-targeting oligomer contains a miR124a binging sequence and a black hole quencher 1 (BHQ1). In the absence of target miR124a, the R9-QD-miR124a beacon forms a partial duplex beacon and remained in quenched state because the BHQ1 quenches the fluorescence signal of the R9-QD-miR124a beacon. The binding of miR124a to the miR124a binding sequence of the miR124a-targeting oligomer triggered the separation of the BHQ1 quencher and subsequent signal-on of a red fluorescence signal. Moreover, enhanced cellular uptake was achieved by conjugation with the R9 peptide, which resulted in increased fluorescent signal of the R9-QD-miR124a beacons in P19 cells during neurogenesis due to the endogenous expression of miR124a.

Reinventing Cell Penetrating Peptides Using Glycosylated Methionine Sulfonium Ion Sequences

Cell penetrating peptides (CPPs) are intriguing molecules that have received much attention, both in terms of mechanistic analysis and as transporters for intracellular therapeutic delivery. Most CPPs contain an abundance of cationic charged residues, typically arginine, where the amino acid compositions, rather than specific sequences, tend to determine their ability to enter cells. Hydrophobic residues are often added to cationic sequences to create efficient CPPs, but typically at the penalty of increased cytotoxicity. Here, we examined polypeptides containing glycosylated, cationic derivatives of methionine, where we found these hydrophilic polypeptides to be surprisingly effective as CPPs and to also possess low cytotoxicity. X-ray analysis of how these new polypeptides interact with lipid membranes revealed that the incorporation of sterically demanding hydrophilic cationic groups in polypeptides is an unprecedented new concept for design of potent CPPs.

Enzyme-Specific Doxorubicin Drug Beacon as Drug-Resistant Theranostic Molecular Probes

We report here on the use of anticancer drug doxorubicin (Dox) to construct a Förster resonance energy transfer (FRET)-based theranostic molecular probe by covalently linking together through a lysine junction a fluorescent drug, a black hole quencher, and a cell-penetrating peptide. We show that upon cleavage by the target lysosomal protease cathepsin B (CatB) the designed drug beacon could release the fluorescent drug serving as an indicator for CatB. Our cell studies suggest that the drug-beacon design can help to circumvent the Dox drug resistance in NCI/ADR-Res ovarian cancer cells, showing significant improvement in cell cytotoxicity compared to the free drug. We believe our design opens up new opportunities to exploit the new functional and structural features of anticancer drugs in addition to their characteristic cytotoxicity.

Peptidic tools applied to redirect alternative splicing events

Peptides are versatile and attractive biomolecules that can be applied to modulate genetic mechanisms like alternative splicing. In this process, a single transcript yields different mature RNAs leading to the production of protein isoforms with diverse or even antagonistic functions. During splicing events, errors can be caused either by mutations present in the genome or by defects or imbalances in regulatory protein factors. In any case, defects in alternative splicing have been related to several genetic diseases including muscular dystrophy, Alzheimer's disease and cancer from almost every origin. One of the most effective approaches to redirect alternative splicing events has been to attach cell-penetrating peptides to oligonucleotides that can modulate a single splicing event and restore correct gene expression. Here, we summarize how natural existing and bioengineered peptides have been applied over the last few years to regulate alternative splicing and genetic expression. Under different genetic and cellular backgrounds, peptides have been shown to function as potent vehicles for splice correction, and their therapeutic benefits have reached clinical trials and patenting stages, emphasizing the use of regulatory peptides as an exciting therapeutic tool for the treatment of different genetic diseases.

Evidence against a role of P-glycoprotein in the clearance of the Alzheimer's disease Aβ1-42 peptides

It has been proposed that the amyloid-β peptides (Aβ) cause the neuronal degeneration in the Alzheimer's disease brain. An imbalance between peptide production at the neuronal level and their elimination across the blood-brain-barrier (BBB) results in peptide accumulation inside the brain. The identification and functional characterization of the transport systems in the BBB with the capacity to transport Aβ is crucial for the understanding of Aβ peptide traffic from the brain to the blood. In this context, it has been suggested that the P-glycoprotein (P-gp), expressed in endothelial cells of the BBB, plays a role in the elimination of Aβ. However, there is little, if any, experimental evidence to support this; therefore, the aim of this investigation was to determine whether P-gp is capable of transporting Aβ peptides. Our results show that ATPase activity measured in plasma membrane vesicles of K562 cells overexpressing P-gp is not increased by the presence of Aβ42, suggesting that Aβ42 is not a P-gp substrate. Similarly, P-gp of pirarubicin was unaffected by Aβ42. Moreover, the overexpression of P-gp does not protect cells against Aβ42 toxicity. Taken together, our results support the conclusion that Aβ42 is not transported by P-gp.

The synaptotagmin juxtamembrane domain is involved in neuroexocytosis

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The highly cationic juxtamembrane segment of synaptotagmin juxtamembrane domain was synthesized.

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This peptide inhibits neurotransmitter release at the neuromuscular junction of mice and Drosophila.

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This peptide localizes mainly on the presynaptic membrane.

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The synaptotagmin juxtamembrane peptide binds monophosphoinositides in a Ca²⁺-independent manner.

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The juxtamembrane segment of synaptotagmin may contribute to the formation of the hemifusion intermediate.

Synaptotagmin is a synaptic vesicle membrane protein which changes conformation upon Ca²⁺ binding and triggers the fast neuroexocytosis that takes place at synapses. We have synthesized a series of peptides corresponding to the sequence of the cytosolic juxtamembrane domain of synaptotagmin, which is highly conserved among different isoforms and animal species, with or without either a hexyl hydrophobic chain or the hexyl group plus a fluorescein moiety. We show that these peptides inhibit neurotransmitter release, that they localize on the presynaptic membrane of the motor axon terminal at the neuromuscular junction and that they bind monophosphoinositides in a Ca²⁺-independent manner. Based on these findings, we propose that the juxtamembrane cytosolic domain of synaptotagmin binds the cytosolic layer of the presynaptic membrane at rest. This binding brings synaptic vesicles and plasma membrane in a very close apposition, favouring the formation of hemifusion intermediates that enable rapid vesicle fusion.

Distinguishing bicontinuous lipid cubic phases from isotropic membrane morphologies using (31)P solid-state NMR spectroscopy

Nonlamellar lipid membranes are frequently induced by proteins that fuse, bend, and cut membranes. Understanding the mechanism of action of these proteins requires the elucidation of the membrane morphologies that they induce. While hexagonal phases and lamellar phases are readily identified by their characteristic solid-state NMR line shapes, bicontinuous lipid cubic phases are more difficult to discern, since the static NMR spectra of cubic-phase lipids consist of an isotropic (31)P or (2)H peak, indistinguishable from the spectra of isotropic membrane morphologies such as micelles and small vesicles. To date, small-angle X-ray scattering is the only method to identify bicontinuous lipid cubic phases. To explore unique NMR signatures of lipid cubic phases, we first describe the orientation distribution of lipid molecules in cubic phases and simulate the static (31)P chemical shift line shapes of oriented cubic-phase membranes in the limit of slow lateral diffusion. We then show that (31)P T2 relaxation times differ significantly between isotropic micelles and cubic-phase membranes: the latter exhibit 2 orders of magnitude shorter T2 relaxation times. These differences are explained by the different time scales of lipid lateral diffusion on the cubic-phase surface versus the time scales of micelle tumbling. Using this relaxation NMR approach, we investigated a DOPE membrane containing the transmembrane domain (TMD) of a viral fusion protein. The static (31)P spectrum of DOPE shows an isotropic peak, whose T2 relaxation times correspond to that of a cubic phase. Thus, the viral fusion protein TMD induces negative Gaussian curvature, which is an intrinsic characteristic of cubic phases, to the DOPE membrane. This curvature induction has important implications to the mechanism of virus-cell fusion. This study establishes a simple NMR diagnostic probe of lipid cubic phases, which is expected to be useful for studying many protein-induced membrane remodeling phenomena in biology.

Delivery of nucleic acids and nanomaterials by cell-penetrating peptides: opportunities and challenges

Many viral and nonviral systems have been developed to aid delivery of biologically active molecules into cells. Among these, cell-penetrating peptides (CPPs) have received increasing attention in the past two decades for biomedical applications. In this review, we focus on opportunities and challenges associated with CPP delivery of nucleic acids and nanomaterials. We first describe the nature of versatile CPPs and their interactions with various types of cargoes. We then discuss in vivo and in vitro delivery of nucleic acids and nanomaterials by CPPs. Studies on the mechanisms of cellular entry and limitations in the methods used are detailed.

Plasma membrane poration by opioid neuropeptides: a possible mechanism of pathological signal transduction

Neuropeptides induce signal transduction across the plasma membrane by acting through cell-surface receptors. The dynorphins, endogenous ligands for opioid receptors, are an exception; they also produce non-receptor-mediated effects causing pain and neurodegeneration. To understand non-receptor mechanism(s), we examined interactions of dynorphins with plasma membrane. Using fluorescence correlation spectroscopy and patch-clamp electrophysiology, we demonstrate that dynorphins accumulate in the membrane and induce a continuum of transient increases in ionic conductance. This phenomenon is consistent with stochastic formation of giant (~2.7 nm estimated diameter) unstructured non-ion-selective membrane pores. The potency of dynorphins to porate the plasma membrane correlates with their pathogenic effects in cellular and animal models. Membrane poration by dynorphins may represent a mechanism of pathological signal transduction. Persistent neuronal excitation by this mechanism may lead to profound neuropathological alterations, including neurodegeneration and cell death.

Polymeric micelles in mucosal drug delivery: Challenges towards clinical translation

Polymeric micelles are nanostructures formed by the self-aggregation of copolymeric amphiphiles above the critical micellar concentration. Due to the flexibility to tailor different molecular features, they have been exploited to encapsulate motley poorly-water soluble therapeutic agents. Moreover, the possibility to combine different amphiphiles in one single aggregate and produce mixed micelles that capitalize on the features of the different components substantially expands the therapeutic potential of these nanocarriers. Despite their proven versatility, polymeric micelles remain elusive to the market and only a few products are currently undergoing advanced clinical trials or reached clinical application, all of them for the therapy of different types of cancer and administration by the intravenous route. At the same time, they emerge as a nanotechnology platform with great potential for non-parenteral mucosal administration. However, for this, the interaction of polymeric micelles with mucus needs to be strengthened. The present review describes the different attempts to develop mucoadhesive polymeric micelles and discusses the challenges faced in the near future for a successful bench-to-bedside translation.

Towards understanding cell penetration by stapled peptides

A systematic study on cell penetration by stapled peptides.

Getting across the cell membrane: an overview for small molecules, peptides, and proteins

The ability to efficiently access cytosolic proteins is desired in both biological research and medicine. However, targeting intracellular proteins is often challenging, because to reach the cytosol, exogenous molecules must first traverse the cell membrane. This review provides a broad overview of how certain molecules are thought to cross this barrier, and what kinds of approaches are being made to enhance the intracellular delivery of those that are impermeable. We first discuss rules that govern the passive permeability of small molecules across the lipid membrane, and mechanisms of membrane transport that have evolved in nature for certain metabolites, peptides, and proteins. Then, we introduce design strategies that have emerged in the development of small molecules and peptides with improved permeability. Finally, intracellular delivery systems that have been engineered for protein payloads are surveyed. Viewpoints from varying disciplines have been brought together to provide a cohesive overview of how the membrane barrier is being overcome.

Enhanced cellular uptake of engineered spider silk particles

Drug delivery systems allow tissue/cell specific targeting of drugs in order to reduce total drug amounts administered to an organism and potential side effects upon systemic drug delivery.

Guanidinium-pendant oligofluorene for rapid and specific identification of antibiotics with membrane-disrupting ability

A new method based on fluorescence resonance energy transfer was developed for specifically screening membrane-disrupting antibiotics.